CPP Check if Type has qdebug stream operator

has_qdebug_stream_operator.cpp

#include <iostream>
#include <QDebug>
#include <QRectF>

template<typename T, typename = void>
struct has_qdebug_stream_operator : std::false_type {};

template<typename T>
struct has_qdebug_stream_operator<T, std::void_t<decltype(std::declval<QDebug>() << std::declval<T>())>> : std::true_type {};

template<typename T>
typename std::enable_if_t<has_qdebug_stream_operator<T>::value>
qprint(T& v) {
    QString s;
    QDebug ds(&s);
    ds << v;
    std::cout << s.toStdString() << std::endl;
};

struct B {};


#define SHOW(...) std::cout << #__VA_ARGS__ << " = " << __VA_ARGS__ << std::endl;

int main(int argc, char* argv[]){
    auto b = QRect(0, 0, 10, 10);
    qprint(b);
    SHOW(has_qdebug_stream_operator<int>::value);
    SHOW(has_qdebug_stream_operator<B>::value);
    return 0;
}

qt_fmt.h

// QT FMT
#include <fmt/ranges.h>
#include <QString>
#include <QStringList>
#include <QRectF>
#include <QDebug>

template <typename T>
constexpr T any_true(const T& t)
{
    return t;
}

// 2.递归函数
template <typename T, typename ... Args>
constexpr T any_true(const T& head, const Args... args)
{
    return head || any_true<T>(args...);
}

template <typename T, typename...X>
struct is_instantiation_of_any {
    static const bool value = any_true(std::is_same_v<T, X>...);
};

template<typename T, typename = void>
struct has_qdebug_stream_operator : std::false_type {};

template<typename T>
struct has_qdebug_stream_operator<T,
        std::enable_if_t<is_instantiation_of_any<T,
                QRect,
                QRectF
        >::value, std::void_t<decltype(std::declval<QDebug>() << std::declval<T>())>>
> : std::true_type {};

// format QString
template <> struct fmt::formatter<QString>: formatter<string_view> {
    auto format(QString s, format_context& ctx) const -> decltype(ctx.out()) {
        return formatter<string_view>::format(qUtf8Printable(s), ctx);
    }
};

// format other qtype
template <typename T>
struct fmt::formatter<T, std::enable_if_t<has_qdebug_stream_operator<T>::value, char>>: formatter<string_view> {
    auto format(const T& t, format_context& ctx) const -> decltype(ctx.out()) {
        QString s;
        QDebug ds(&s);
        ds << t;
        return formatter<string_view>::format(qUtf8Printable(s), ctx);
    }
};

#define QFMT(...) QString::fromStdString(fmt::format(## __VA_ARGS__))
#define CFMT(...) fmt::format(## __VA_ARGS__).c_str()